1. Field of the Invention
The present invention relates to a fiber optic cable. More particularly, the invention relates to a fiber optic indoor/outdoor tight buffered cable.
2. Description of the Related Art
Fiber optic indoor/outdoor tight buffered cable is commonly employed for intra-building network applications, for example, for interconnecting between one central office and other offices. In general, optical fiber has advantages as compared with metallic cord in that it has a smaller diameter and a wider bandwidth. A disadvantage of optical fiber is that it is more vulnerable not only to tension in its longitudinal direction but also to external impact in its widthwise direction.
FIG. 1 is a cross-sectional view of a conventional fiber optic indoor/outdoor tight buffered cable. FIG. 2 is a side view of the fiber optic cable shown in FIG. 1. The fiber optic cable comprises a central strength member 110, nine inner tight buffered cores 120, fifteen outer tight buffered cores 130, an outer strength member 140 and a jacket 150.
The central strength member 110 is disposed at the center of the fiber optic cable so as to provide tensile strength.
The nine inner tight buffered cores 120 are disclosed, for example, in U.S. patent application Ser. No. 946,646, filed Dec. 22, 1986, and U.S. Pat. No. 4,781,433 issued Nov. 1, 1988 to Arroyo et al. incorporated by reference in their entirety. Both patents disclose an inner tight buffered core comprising a core 132, a cladding 134 and a tight buffered layer 136. In addition, the nine inner tight buffered cores 120 are disposed in a spiral form around the central strength member 110. That is to say, the nine inner tight buffered cores 120 are spirally twisted at a predetermined pitch.
The fifteen outer tight buffered cores 130 are also disposed in a spiral form to enclose the nine inner tight buffered cores 120. Therefore, the fifteen outer tight buffered cores 130 are spirally twisted at a predetermined pitch.
The outer strength member 140 is spirally wrapped to enclose the outer tight buffered cores 130, performing a damping function under external pressure.
The jacket 150 is formed around the circumference of the fiber optic cable by an extrusion process, in order to protect the interior of the cable from external environments.
A drawback of the fiber optic cable described above is that when the inner and outer tight buffered cores 120 and 130 are disposed in the same direction, they are disarrayed or have a poor flexible property. Furthermore, another drawback is that such a fiber optic cable is inefficient to produce owing to complicated production steps.
Therefore, there is a need in the art for a fiber optic cable which overcomes the afore-stated problems.